1. Field of the Invention
The present invention relates to a process for producing a resinous hose formed from a thermoplastic resin and having bent portions.
2. Description of the Related Art
A bendable rubber hose is conventionally used as a radiator hose for an automobile, which is required to be mounted to extend within a narrow engine room. Alternatively, various hoses made from a resin material that is lightweight as compared with the rubber have been proposed. For example, Japanese Patent Application Laid-open No. 7-71663 discloses a radiator hose used by bending a flexible resinous hose having a bellows-shaped unevenness formed thereon into a predetermined shape.
However, the conventional radiator hose described in Japanese Patent Application Laid-open No. 7-71663 suffers from the following problem: The resinous hose is arranged in the elastically bent state. For this reason, when the internal pressure of cooling water is applied to the resinous hose, the bent resinous hose is stretched to the original rectilinear shape and hence, the shape of the hose is not stable.
Therefore, it is conceived that a resinous hose having the bellows-shaped unevenness formed thereon is plastically deformed into the shape of use, so that the shape at the time of application of the internal pressure is stabilized. To plastically deform the resinous hose having the bellows-shaped unevenness formed thereon into a desired shape, a coil spring may be inserted into the heated resinous hose, or a pressure may be applied to the inside of the resinous hose, thereby applying an external force to the hose to bend the hose, while preventing the hose from being crushed. Then, the hose may be cooled and solidified and thereafter, the coil spring may be withdrawn, or the internal pressure may be removed. Another method is to insert a resinous hose having the bellows-shaped unevenness formed thereon into a die, and then heat the die to form the resinous hose having the desired shape.
However, a resinous hose bent by the above methods suffers from the following problem: The steps of producing such hoses are not only complicated and increase the cost, but also when the resinous hose is used in a high-temperature and a high-pressure environment, as is the case with the radiator hose, the pleats of the bellows are stretched by a creep phenomenon, whereby the bent shape is gradually varied.
Accordingly, it is an object of the present invention to provide a resinous hose at a low cost, wherein even if the hose is used in a high-temperature and high-pressure environment, the bent shape thereof can be maintained over a long period of time.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided a process for producing a resinous hose formed from a thermoplastic resin having cylindrical portions extending rectilinearly, and a bent bellows portion, the process comprising a first step of forming a cylindrical hose by extrusion, a second step of forming a bellows portion which has pleats each shaped to be differentiated circumferentially, at least at a lengthwise portion of the extruded hose, a third step of heating the hose having the bellows portion formed thereon into a plastic state, and a fourth step of bending the hose by applying a pressure to an inside of the hose heated into the plastic state, thereby stretching the pleats of the bellows portion, and a fifth step of cooling the bent hose.
With the above process, the bellows portion which has pleats differentiated circumferentially in shape are formed at least at a lengthwise portion of the extruded hose, and the pressure is applied to the inside of the hose in the heated state to stretch the pleats of the bellows portion, thereby bending the hose. Therefore, any portions of the hose can be bent through any angles in any directions by only changing the positions of the bellows portion, the shapes and the numbers of the pleats and the like. In addition, the bellows portion can be bent only by heating and pressurizing the hose and hence, special equipment is not required, leading to a reduced manufacture cost. Moreover, the pleats of the bellows portion of the completed hose are almost stretched out, whereby the bellows structure is lost. Therefore, even if the hose is exposed to a high temperature and a high pressure, the bent angle of the bellows portion is not varied, and hence, the shape of the hose can be maintained over a long period of time.
According to a second aspect and feature of the present invention, in addition to the first feature, the bellows portion of the hose formed in the second step includes a bellows wall having continuous crests and valleys, and a non-bellows wall located on the side diametrically opposite to the bellows wall. Additionally, in the second step, a portion of the cylindrical hose formed in the first step is displaced radially inwards to form the valleys on the bellows wall, and a portion of the cylindrical hose is displaced radially outwards to form the non-bellows wall.
With the above feature, a portion of the cylindrical hose is displaced radially inwards to form the valleys of the bellows wall, and a portion of the cylindrical hose is displaced radially outwards to form the non-bellows wall in the second step. Therefore, the decrease in thickness of the bellows wall that may be thinned during the formation can be suppressed to the minimum, and the thickness of the non-bellows wall that may be thickened during the formation can be positively decreased, whereby the thickness of the bellows portion of the entire hose can be uniform over the entire region. Thus, durability can be enhanced without increasing the weight of the hose and without decreasing the sectional area of a flow path.
According to a third aspect and feature of the present invention, there is provided a resinous hose formed in the second step of a process for producing a resinous hose according to the first feature, wherein the bellows portion includes a bellows wall having continuous crests and valleys, and a non-bellows wall located on the side diametrically opposite to the bellows wall, the outside diameter of the valleys of the bellows wall being smaller than the outside diameter of the cylindrical portions, and the outside diameter of the non-bellows wall being larger than the outside diameter of the cylindrical portions.
With the above feature, the outside diameter of the valleys of the bellows wall is smaller than the outside diameter of the cylindrical portions, and the outside diameter of the non-bellows wall is larger than the outside diameter of the cylindrical portions. Therefore, the decrease in thickness of the bellows wall that may be thinned during the formation can be suppressed to the minimum, and the thickness of the non-bellows wall that may be thickened during the formation can be positively decreased, whereby the thickness of the bellows portion of the hose can be uniform over the entire region. Thus, the durability can be enhanced without increasing the weight of the hose and without decreasing the sectional area of a flow path.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings.